Rotary anode for an x-ray tube

ABSTRACT

A rotary anode of an X-ray tube delivers X-rays from at least the surface struck by electrons and consisting mostly of molybdenum. According to the present invention this surface consists to at least 90 percent of molybdenum and up to 10 percent hafnium.

nited States Patent Friedel et al.

ROTARY ANODE FOR AN X-RAY TUBE Inventors: Rudolf Friedel, Erlangen, Germany;

Karl Sedlatschek, Reutte, Austria Assignee: Siemens Aktiengesellschaft,

Erlangen, Germany Filed: June 12, 1973 Appl. 190.; 369,393

Foreign Application Priority Data June 28, 1972 Germany 2231686 US. Cl 313/330, 75/123 J, 75/176,

313/55,313/311 Int. Cl. H01j /08 Field of Search 313/330, 31 l, 55, /123 1, 134 V, 176

[ Mar. 4, 1975 [56} References Cited UNITED STATES PATENTS 3,169,860 2/1965 Semchyshen 75/176 3,689,795 9/1972 Benesovsky 313/330 3,737,699 6/1973 Gager 313/330 Primary Examiner-James W.- Lawrence Assistant E.\'aminer--SaXfie1d Chatmon, Jr. Attorney, Agent, or FirmRichards & Geier [57] ABSTRACT A rotary anode of an X-ray tube delivers X-rays from at least the surface struck by electrons and consisting mostly of molybdenum. According to the present invention this surface consists to at least percent of molybdenum and up to 10 percent hafnium.

3 Claims, 2 Drawing Figures 1 ROTARY ANODE FOR AN X-RAY TUBE This invention relates to a rotary anode of an X-ray tube which delivers X-rays from at least the surface struck by electrons and consisting mostly of molybde num.

Such anodes are used primarily in soft ray diagnosis, for example, in examination of female breasts.

It is known to use X-ray tubes anodes having surfaces which are struck by electrons and thus excited for the sending of X-rays, which are made of molybdenum or a molybdenum alloy, so as to produce rays of a wave length preferred for a specific purpose.

A drawback is that anodes made of molybdenum or molybdenum alloys have a quick drop in ray delivery. This drop shows outwardly in the anodes in the form of a roughened surface.

An object of the present invention is to eliminate at least to a great extent the drop in the ray production and its cause, namely, the roughened surface.

The present invention pertains to a rotary anode of an X-ray tube which produces X-rays at locations struck by electrons and consisting primarily of molybdenum. In the accomplishment of the objectives of the present invention it was found desirable to make the struck surface of at least 90 percent of molybdenum and up to percent of hafnium. Alloys of this type are much less subject to formation of cracks, since the inclination to thermal fatigue is diminished.

According to an embodiment of the present invention the rotary anode is a compound body consisting of a plate having a thickness of about 10 mm of molybdenum or another material resistant to high temperatures, for example, graphite, which is coated with a layer having usually the thickness of l to 2 mm and consisting of a molybdenum-hafnium.alloy. When a supporting body of graphite is used, it is advantageous to apply a diffusion diminishing intermediate layer. for example of tantalum, before applying the alloy. The anode can also be a single body consisting of a molybdenumhafnium alloy. For the special use in female breasts examination it is best to use an alloy of 95 percent molybdenum and 5 percent hafnium. Larger additions are also possible and very advantageous for diminishing the rawness, but they falsify the molybdenum ray formation to a too great an extent, namely, an excessive amount of hard rays is produced. The addition of haf nium as an alloy part of molybdenum in accordance with the present invention has very good results concerning the diminution of rawness without producing any noticeably worse contrast of X-ray exposure. Even 1% of hafnium in the alloy substantially diminishes the rawness of molybdenum, so that a continuously im proved ray output is produced.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawing showing by way of example only, preferred embodiments of the inventive idea.

In the drawing:

FIG. 1 is a side view partly in section of an X-ray tube with a rotary anode carrying a molybdenum alloy at the focal point path.

FIG. 2 is section through a rotary anode for use with the tube shown in FIG. 1.

FIG. 1 shows an X-ray tube 2 with a container I having at one end the cathode arrangement 3 and at the other end the anode arrangement 4. The cathode de vice is fixed by a sleeve 5 to one end of the container 1 and has a shoulder 6 carrying the actual glow cathode. Opposite the cathode device at the other end of the tube container 1 is the anode device carrying a rotor 7 for driving the rotary anode 9 connected with it by an axle 8. The rotary anode consists of a plate 10 which is 10 mm thick and consists of an alloy of molybdenum with 5 percent tungsten. The plate I0 is pressed by a screw 11 against a bearing'l2 of the axle 8; it can be rotated by the rotor 7 and a stator (not shown). The outer surface of the plate 10 directed to the cathode device 3 has an annular zone located upon its outer edge and carrying acoating 13 which has a thickness of 1 mm and which consists of an alloy containing 95 percent molybdenum and 5 percent hafnium. When a corresponding voltage is provided between the lines 15, 16 and 17 and the support 18, electrons are produced from the glow cathode l4 and strike this coating. These electrons release X-rays in the focal point paths l9 and 20 individually or jointly, depending upon the manner in which the cathode is operated, the X-rays being used in X-ray technology.

When graphite is used in the making of the plate 10, an intermediate layer 21 of tantalum which delays diffusion and has a thickness of ,u. is introduced between the plate 10 and the layer 13.

What is claimed is:

l. A rotary anode for an X-ray tube having a surface struck by electrons and producing X-rays, said surface consisting of 95 percent molybdenum and 5 percent hafnium.

2. A rotary anode for an X-ray tube having a surface struck by electrons and producing X-rays, said surface containing up to 10 percent hafmium and a' balance of molybclemum comprising a body consisting of graphite covered with a diffusion delaying intermediate layer between said body and the said surface consisting of a molybdenum-hafnium alloy.

3. A rotary anode for an X-ray tube having a surface struck by electrons and producing X-rays, said surface containing up to 10 percent hafmium and a balance of molybclemum comprising a body consisting of graphite covered with a diffusing delaying intermediate layer consisting of tantalum which is covered with a layer of 

1. A ROTARY ANODE FOR AN X-RAY TUBE HAVING A SURFACE STRUCK BY ELECTRONS AND PRODUCING X-RAYS, SAID SURFACE CONSISTING OF 95 PERCENT MOLYBDENUM AND 5 PERCENT HAFNIUM.
 2. A rotary anode for an X-ray tube having a surface struck by electrons and producing X-rays, said surface containing up to 10 percent hafmium and a balance of molybclemum comprising a body consisting of graphite covered with a diffusion delaying intermediate layer between said body and the said surface consisting of a molybdenum-hafnium alloy.
 3. A rotary anode for an X-ray tube having a surface struck by electrons and producing X-rays, said surface containing up to 10 percent hafmium and a balance of molybdemum comprising a body consisting of graphite covered with a diffusing delaying intermediate layer consisting of tantalum which is covered with a layer of molybdenum-hafnium alloy. 